Acrylic release agent precursor, release agent article, and process for producing release agent article

ABSTRACT

The present invention provides an acrylic release agent precursor, which makes it possible to prepare an acrylic release agent efficiently as much as possible in a comparatively small ultraviolet dose, regardless of the component. An acrylic release agent precursor which contains a poly(meth)acrylate ester having a group capable of being activated by ultraviolet radiation and has a storage elastic modulus of 1×10 2  to 3×10 6  Pa at 20° C. and a frequency of 1 Hz, wherein said precursor, after irradiation with ultraviolet radiation, has a contact angle of 15° or more to a mixed solution of methanol and water (volume ratio of 90/10) having wetting tension of 25.4 N/m.

FIELD

The present invention relates to a release agent precursor containing apolymer such as poly(meth)acrylate ester, a release agent article usingthe same, and a process for producing the same.

BACKGROUND

An adhesive tape and an adhesive sheet are obtained by forming anadhesive on a surface of a substrate and are usually stored after takingup in a roll form. In that case, the back surface of the substrate isgenerally coated with a release agent to protect the adhesive surface ofthe adhesive tape or adhesive sheet. When using the adhesive tape oradhesive sheet, it can be easily unwound. Alternatively, the adhesivesurface is covered with a separate substrate coated with a releaseagent, thereby to protect the adhesive surface.

Various types of release agents have been known. Particularly, a releaseagent having a long-chain alkyl group (long-chain alkyl-based releaseagent) is useful in the electronic industry because it is comparativelycheap and is less likely to cause contamination.

One example of the long-chain alkyl release agents is disclosed in thepamphlet of International Publication WO 01/64805 and/or KOKAI (JapaneseUnexamined Patent Publication) No. 2001-240775. Each of these long-chainalkyl release agents is an acrylic release agent comprising a productobtained by irradiating an acrylic release agent precursor, whichcontains a poly(meth)acrylate ester and has a storage elastic modulus of1×10² to 3×10⁶ Pa at 20° C. and a frequency of 1 Hz, with ultravioletradiation, said acrylic release agent having a contact angle of 15° ormore with a mixed solution of methanol and water (volume ratio of 90/10)having a wetting tension of 25.4 N/m. This acrylic release agent hascomparatively high adhesion with a substrate made of polyethyleneterephthalate after applying on the substrate. This acrylic releaseagent can maintain a comparatively low peel force from apressure-sensitive adhesive such as acrylic pressure sensitive adhesiveeven when exposed to high temperature. Furthermore, this acrylic releaseagent substantially has no influence on the residual adhesion of theadhesive.

As is apparent from the above description, the acrylic release agentdescribed above is prepared by passing through the step of irradiatingthe acrylic release agent precursor with ultraviolet radiation. However,the ultraviolet irradiation dose required in this step varies widelydepending on the composition of the acrylic release agent precursor.When the composition which requires a small dose to form a release agentis compared with the composition which requires a large dose, the dosevaries sometimes by 3 to 5 times.

SUMMARY

It is desirable in the preparation of the acrylic release agent thatthere be (1) no significant change in the required ultravioletirradiation dose depending on composition of the acrylic release agentprecursor and (2) a reduction in ultraviolet irradiation dose in view ofan increase in productivity.

The present invention is directed to providing an acrylic release agentprecursor, which makes it possible to prepare an acrylic release agenthaving the above-mentioned releasability as efficiently as possible in acomparatively small ultraviolet dose. Additionally, the presentinvention provides a release agent article using the acrylic releaseagent precursor, and a process for producing the same.

The present invention provides an acrylic release agent precursor whichcontains a poly(meth)acrylate ester having a group capable of beingactivated by ultraviolet radiation (also referred to as “an ultravioletactive group”) and has a storage elastic modulus of 1×10² to 3×10⁶ Pa at20° C. and a frequency of 1 Hz, wherein said precursor, afterirradiation with ultraviolet irradiation, has a contact angle of 15° ormore to a mixed solution of methanol and water (volume ratio of 90/10)having a wetting tension of 25.4 N/m.

A release agent article is provided by forming the release agentprecursor on a substrate and irradiating the release agent precursorwith ultraviolet irradiation.

When using the acrylic release agent precursor described above, itbecomes possible to efficiently prepare an acrylic release agent.

Generally, when using a mixture of a poly(meth)acrylate ester and a freeradical generating agent having an ultraviolet active group, theultraviolet irradiation dose can not be reduced in order to prepare theacrylic release agent. Therefore, the poly(meth)acrylate ester having anultraviolet active group used in the present invention is essentiallydifferent from a simple mixture of a poly(meth)acrylate ester and a freeradical generating agent having an ultraviolet active group.

The present invention will be explained by way of preferred embodiments.As will be apparent to a person with an ordinary skill in the art, thepresent invention is not limited to these embodiments described indetail.

As used herein, the term “contact angle” is defined as a value of acontact angle as measured by a mixed solution (volume ratio of 90/10)having a wetting tension of 25.4 N/m described in JIS K6768: 1999. Thismeasurement is conducted under the conditions of a temperature of 23±1°C. and a relative humidity of 50±5%.

As used herein, the storage elastic modulus (G′) of the acrylic releaseagent precursor is a value as measured at 20° C. and a frequency of 1 Hzin a shear mode, using a viscoelasticity meter (for example, DynamicAnalyzer RDA II manufactured by Rheometrics).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one embodiment of a releasesheet or a release tape of the present invention.

DETAILED DESCRIPTION

The acrylic release agent precursor of the present invention is apolymer composition containing a polymer such as poly(meth)acrylateester having an ultraviolet active group.

The poly(meth)acrylate is, for example, a copolymer formed from anacrylic monomer component containing a (meth)acrylate having C₁₂₋₃₀alkyl group (hereinafter also referred to as a “first alkyl(meth)acrylate”) and a (meth)acrylate having C₁₋₁₂ alkyl group(hereinafter also referred to as a “second alkyl (meth)acrylate”), and a(meth)acrylate ester having an ultraviolet active group.

In this case, the alkyl group of the first alkyl (meth)acrylateconstitutes a comparatively long side chain in the copolymer. Such along alkyl side chain is effective to reduce a surface energy of theacrylic release agent. This surface energy is estimated by the “contactangle” as described above.

Preferred long alkyl side chain does not have a polar functional groupsuch as carboxyl group, hydroxyl group, or nitrogen- orphosphorus-containing group. Although the long alkyl side chain canusually maintain a comparatively low peel force at low temperature andhigh temperature, it is difficult to maintain at a comparatively lowpeel force when a release agent having the polar functional group isexposed to high temperature. Preferred first alkyl (meth)acrylatecontaining a long alkyl side chain includes lauryl (meth)acrylate, cetyl(meth)acrylate, stearyl (meth)acrylate, or behenyl (meth)acrylate.

The alkyl group of the second alkyl (meth)acrylate constitutes acomparatively short side chain in the copolymer described above. Such ashort alkyl side chain can reduce the glass transition temperature ofthe release agent precursor to 30° C. or lower. As a result, it can alsoreduce the storage elastic modulus to a value within a range from 1×10²to 3×10⁶ Pa, thus making it possible to provide smooth peeling from apressure-sensitive adhesive to the acrylic release agent. Preferredshort alkyl side chain does not have the polar functional groupdescribed above, similar to the alkyl side chain of the first alkyl(meth)acrylate.

The copolymer does not limit the amount of two kinds of acrylic monomercomponents described above is not usually limited, but contains thefirst alkyl (meth)acrylate or second alkyl (meth)acrylate in the amountwithin a range from 10 to 90% by weight based on the total weight of thefirst alkyl (meth)acrylate and second alkyl (meth)acrylate. When theamount of the first alkyl (meth)acrylate exceeds about 90% by weight,the acrylic release agent has comparatively high crystallinity as aresult of a strong influence of the first alkyl (meth)acrylate and tendsto provide jerky peel. On the other hand, when the amount of the secondalkyl (meth)acrylate exceeds about 90% by weight, the acrylic releaseagent, tends to provide a comparatively high peel force, as a result ofa strong influence of the second alkyl (meth)acrylate.

According to the present invention, both of the first alkyl(meth)acrylate and the second alkyl (meth)acrylate have a C₁₂ alkylgroup.

In another aspect, it can be said that the poly(meth)acrylate ester isderived from a monomer component containing an alkyl (meth)acrylatehaving a branched C₈₋₃₀ alkyl group, and a (meth)acrylate ester havingan ultraviolet active group. Examples of the alkyl (meth)acrylate havinga branched C₈₋₃₀ alkyl group include 2-ethylhexyl (meth)acrylate,2-hexyldodecyl acrylate, 2-heptylundeceyl acrylate, 2-octyldecylacrylate, and isononyl (meth)acrylate. Such a (meth)acrylate having abranched side chain can reduce the storage elastic modulus and surfaceenergy by lowering the crystallinity itself. Thus, it is not necessaryfor the acrylic release agent precursor to contain two components suchas first alkyl (meth)acrylate and second alkyl (meth)acrylate describedabove as far as it has a branched C₈₋₃₀ alkyl group. The polymer of2-hexyldecyl acrylate or 2-octyldecyl acrylate constitutes a preferredacrylic release agent precursor because it can simply reduce the surfaceenergy of the release agent.

According to the present invention, as described above, thepoly(meth)acrylate ester has an ultraviolet active group. Thisultraviolet active group can generate a free radical in the releaseagent precursor by irradiation with ultraviolet radiation. The generatedfree radical promotes crosslinking of the release agent precursor andadhesion to the substrate, resulting in an improvement in adhesionbetween the substrate and the release agent. As far as the object andeffect of the present invention is achieved, the ultraviolet activegroup is not specifically limited, but is preferably those derived frombenzophenone or acetophenone. Introduction of the ultraviolet activegroup into the poly(meth)acrylate ester can be conducted byincorporating a (meth)acrylate ester having an ultraviolet active groupas a monomer component and polymerizing the monomer component containingthe (meth)acrylate ester. A preferred amount of the (meth)acrylate esterhaving an ultraviolet active group is within a range from 0.01 to 1.0%by weight per poly(meth)acrylate ester unit. When the amount of the(meth)acrylate ester having an ultraviolet active group is lower than0.01% by weight, there is a tendency that a substantial effect ofreducing the ultraviolet irradiation dose required to form the releaseagent can not be obtained. Even if the amount of the (meth)acrylateester having an ultraviolet active group is greater than 1.0% by weight,the effect is already sufficient under conventional conditions ofirradiation with ultraviolet radiation and an influence of the additionof a new component is likely to be exerted on the peel force.

The polymer of the acrylic release agent precursor preferably has aweight-average molecular weight within a range from 100,000 to2,000,000. When the polymer has a weight-average molecular weight oflower than about 100,000, the resulting acrylic release agent precursorhas an undesirable high peel force. When the polymer has aweight-average molecular weight of greater than about 2,000,000,satisfactory peel performances are obtained, however, it tends to becomedifficult to treat the polymer during polymerization reaction describedhereinafter because of its high viscosity.

The monomer component described above can be usually polymerized in thepresence of a predetermined amount of a polymerization initiator,thereby to form an acrylic release agent precursor. Preferredpolymerization is solution polymerization. This solution polymerizationcan be usually conducted in the state where the monomer component isdissolved in a solvent, together with the polymerization initiator, inan atmosphere of an inert gas such as nitrogen at 50 to 100° C. As aresult, the solution of the polymer as a reaction product can be used asit is after the completion of the polymerization. As the solvent, forexample ethyl acetate, methyl ethyl ketone or heptane can be used. Ifnecessary, the molecular weight of the polymer may be controlled to theabove-described range by adding a chain transfer agent to the solvent.

The polymerization initiator is not specifically limited. For example,an azobis compound such as 2,2′-azobisisobutyronitrile,2,2′-azobis(2-methylbutyronitrile) or2,2′-azobis(2,4-dimethylvaleronitrile) and a peroxide such as benzoylperoxide or lauroyl peroxide may be used as the polymerizationinitiator. Particularly, 2,2′-azobisisobutyronitrile and2,2′-azobis(2-methylbutyronitrile) are commercially available from WakoPure Chemicals Industries, Ltd. under the trade name of V-60 and V-59.Preferably, the polymerization initiator is used in the amount within arange from 0.005 to 0.5% by weight based on the total weight of themonomer component. When the amount of the polymerization initiator islower than about 0.005% by weight, the polymerization reaction tends toproceed comparatively slowly. On the other hand, when the amount of thepolymerization initiator is greater than about 0.5% by weight, theresulting acrylic release agent precursor tends to have a comparativelylow molecular weight.

The acrylic release agent precursor as described above is converted intoan acrylic release agent by irradiating with ultraviolet radiation,after the precursor is coated on a substrate. This acrylic release agenthas a contact angle of 15° or more to a mixed solution of methanol andwater (volume ratio of 90/10) having a wetting tension of 25.4 N/m. Sucha contact angle is advantageous, since it effectively inhibits apressure-sensitive adhesive from wetting and spreading over the surfaceof the acrylic release agent and also reduces the affinity with theadhesive.

Also this acrylic release agent can provide a certain, comparatively lowpeel force of 0.05 to 3 N/25 mm to a pressure-sensitive adhesive such asan acrylic pressure-sensitive adhesive. Such a peel force isadvantageous to easily peel a release sheet from an adhesive tape or anadhesive sheet. Preferably, the acrylic release agent has a peel forceof lower than 0.2 N/25 mm, as measured by the process described in theexamples, to a general acrylic pressure-sensitive adhesive such as theacrylic pressure-sensitive adhesive in the examples describedhereinafter.

In FIG. 1, a cross-sectional view of one embodiment of a release sheet(or a release tape) as a release agent article of the present inventionis shown. This release sheet (1) is composed of a substrate (2) and anacrylic release agent (3) formed on the substrate (2). This acrylicrelease agent (3) is obtained by irradiating the acrylic release agentprecursor of the present invention with ultraviolet radiation. Usually,this acrylic release agent is formed on the substrate in the thicknesswithin a range from 0.01 to 1 μm. The acrylic release agent is generallyobtained by irradiating with ultraviolet radiation after coating withthe acrylic release agent precursor. As disclosed in the pamphlet ofInternational Publication WO 01/64805 and/or KOKAI (Japanese UnexaminedPatent Publication) No. 2001-240775, the acrylic release agent adheresto the substrate by the irradiation with ultraviolet radiation, eventhough the acrylic release agent has no polar functional group. As thesubstrate, for example, a film made of plastic such as polyester orpolyolefin (for example, polyethylene terephthalate, polyethylenenaphthalate or polybutylene terephthalate) or a paper can be used.Preferred thickness of the substrate is within a range from 10 to 300μm.

Usually, the acrylic release agent precursor is produced by the solutionpolymerization as described above and exists in the state of a polymersolution. Therefore, the substrate is coated with the polymer solutionin the thickness within a range from 0.01 to 1 μm, and preferably from0.05 to 0.5 μm, using a coating means such as bar coater. When thethickness is lower than 0.01 μm, it is difficult to form a uniformcoating and the peel force of the acrylic release agent tends to beincreased. Even if the thickness exceeds about 1 μm, an influence ishardly exerted on the peel force of the acrylic release agent. Ifnecessary, the polymer solution may be applied after diluting with adiluent until a predetermined viscosity is achieved. Examples if thediluent include ethyl acetate, butyl acetate, methyl ethyl ketone,methyl isobutyl ketone, hexane, heptane, toluene, xylene and/ormethylene chloride.

The acrylic release agent precursor applied as described above isconverted into an acrylic release agent by irradiation with ultravioletradiation. Unlike electron beam, it is not necessary to irradiate withultraviolet radiation under reduced pressure on in an atmosphere of aninert gas such as nitrogen. Therefore, the irradiation with ultravioletradiation becomes easier than that with electron beam. Such an acrylicrelease agent can adhere closely to the substrate as described above.According to the present invention, the dose of irradiation withultraviolet radiation varies depending on the kind and structure of thepoly(meth)acrylate, but may be a given low dose within a range from 10to 100 mJ/cm². As described above, the poly(meth)acrylate of thisacrylic release agent precursor has an ultraviolet active group.Therefore, the release agent article can be efficiently produced in ashort time.

The present invention was explained by way of preferred embodiments, butthe present invention is not limited thereto.

The poly(meth)acrylate ester may be derived from a plurality of monomercomponents. For example, the first alkyl (meth)acrylate and second alkyl(meth)acrylate may be derived from a plurality of monomer components,respectively.

Usually, the monomer component has no polar functional group on the sidechain. However, the monomer component may have a polar functional groupon the side chain as far as the acrylic release agent precursor and theacrylic release agent have the storage elastic modulus and contact angledescribed above.

EXAMPLES

The present invention will now be explained in detail by way ofexamples. As will be apparent to a person with an ordinary skill in theart, the present invention is not limited to these examples. In thefollowing examples, “parts” are by weight unless otherwise specified.

Production of Release Agent Article Example 1

First, 100 parts of an NK ester ISA manufactured by OSAKA ORGANICCHEMICAL INDUSTRY LTD. and 0.03 parts of EBECRYL P36 manufactured byDAICEL-UCB COMPANY LTD. were added as monomer components to a mixedsolvent containing ethyl acetate and n-heptane in a weight ratio of50:50 to prepare a reaction solution having a solid content of 50% byweight. The NK ester ISA is a mixture of 2-octyldecyl acrylate and2-hexyldodecyl acrylate in a weight ratio of 1:1 and is also referred toas 2-heptylundeceyl acrylate (see the pamphlet of InternationalPublication WO 01/64085). Also EBECRYL P36 is an acrylate ester havingan ultraviolet active group derived from benzophenone. Then, 0.004 partsof an initiator consisting of 2,2′-azobis(2,4 dimethylvaleronitrile) wasadded in a reaction vessel. This initiator is commercially availablefrom Wako Pure Chemicals Industries, Ltd. under the trade name of V-65.

Then, the interior of this reaction vessel was purged with a nitrogengas for 10 minutes. This reaction vessel was transferred in a rotaryconstant-temperature bath maintained at 50° C. and then allowed to standtherein for 20 hours. At this time, the monomer component in the vesselwas reacted to produce a release agent precursor made of an acryliccopolymer. The storage elastic modulus of the resulting release agentprecursor was measured as described hereinafter.

The acrylic release agent precursor was diluted with ethyl acetate toprepare a diluted solution having a solid content of 1% by weightwithout being separated from the solution. A 50 μm thick substrate madeof polyethylene terephthalate (PET) was coated with the dilutedsolution, using a bar coater, dried to remove ethyl acetate andn-heptane, and then dried to obtain an acrylic release agent precursorhaving a thickness of about 0.1 μm.

Using a high-pressure mercury lamp (H type-valve) manufactured by FusionSystem Corporation, the acrylic release agent precursor was irradiatedwith ultraviolet radiation in an energy density shown in Table 1 toobtain a sheet-like release agent article (hereinafter referred to as a“release sheet”). The peel force and contact angle of the release sheetthus obtained were measured as described hereinafter.

Example 2

In the same manner as in Example 1, except that 100 parts of an NK esterISA and 0.1 parts of EBECRYL P36 manufactured by DAICEL-UCB COMPANY LTD.were added in this example, a release sheet was produced and evaluated.

Example 3

In the same manner as in Example 1, except that 100 parts of an NK esterISA and 0.4 parts of EBECRYL P36 manufactured by DAICEL-UCB COMPANY LTD.were added in this example, a release sheet was produced and evaluated.

Example 4

In the same manner as in Example 1, except that 100 parts of an NK esterISA and 0.8 parts of EBECRYL P36 manufactured by DAICEL-UCB COMPANY LTD.were added in this example, a release sheet was produced and evaluated.

Comparative Example 1

In the same manner as in Example 1, except that EBECRYL P36 was not usedin this example, a release sheet was produced and evaluated.

Storage Elastic Modulus of Release Agent Precursor

The storage elastic modulus of the respective release agent precursorsdescribed above was measured at 20° C. and a frequency of 1 Hz in ashear mode, using a viscoelasticity meter (for example, Dynamic AnalyzerRDA II manufactured by Rheometrics). The storage elastic modulus ofthese release agent precursors is shown in Table 1.

Peel Force of Release Agent Article

The peel force of the respective release sheets described above wasdetermined in the following manner, using an acrylic pressure-sensitiveadhesive sheet obtained by crosslinking a polymer derived from a monomercomponent containing butyl acrylate, acrylic acid and vinyl acetate in aweight ratio of 100:8:1.5 with 1% by weight of isophorone diisocyanate.

An acrylic pressure-sensitive adhesive sheet was stuck on a releasesheet and then allowed to stand in an oven at 110° C. for 6 hours. Therelease sheet was taken out from the oven, together with the acrylicadhesive sheet, and then allowed to stand at room temperature (25° C.)overnight. When the release sheet was continuously peeled off from theacrylic adhesive sheet at a peel angle of 180° and a peeling rate of 300mm/min. in a width of 25 mm using Autograph (AGS-100B) manufactured byShimadzu Corp., a load applied to the release sheet was measured and theresulting load was taken as a peel force. The peel forces of the releasesheets at various acrylic release agent precursors and ultravioletenergy densities are shown in Table 1.

Contact Angle of Release Agent

The contact angle of the release sheet was measured by using a contactangle meter CA-A manufactured by Kyowa Interface Science Co., LTD. Inthe measurement, a mixed solution of methanol and water (volume ratio of90/10) having a wetting tension of 25.4 N/m described in JIS K6768: 1999was used. At this time, the measurement was conducted within 5 secondsafter the dropwise addition. The contact angles of the release sheets atvarious acrylic release agent precursors and ultraviolet energydensities are shown in Table 1.

TABLE 1 Example No. Comparative Example 1 Example 2 Example 3 Example 4Example 1 Composition ISA/P36 (wt %/wt %) 100/0.03 100/0.1 100/0.4100/0.8 100/0 Storage elastic modulus (Pa) of release agent precursor UVdose (mJ/cm²) 1.7 × 10³ 1.4 × 10³ 2.2 × 10³ 1.5 × 10³ 1.2 × 10³ Peelforce (N/25 mm) 10 — — 16.7  7.9 — 20 — —  8.1  0.17 — 30 — —  0.16 0.16 — 40  6.6  3.1  0.16  0.16  7.9 60  0.97  0.16  0.16  0.16  3.6 80 0.16  0.15  0.15  0.16  1.9 100  0.16  0.15 — —  0.16 120  0.15  0.16 ——  0.17 200  0.15  0.16 — —  0.16 300 — — — —  0.17 Contact angle 1042.0 41.1 40.7 41.4 39.9 (degree) 20 41.3 41.3 40.5 41.0 39.7 30 41.541.4 40.1 41.1 39.9 40 41.3 41.1 39.7 41.1 39.8 60 41.1 40.5 39.5 40.639.1 80 40.4 40.2 38.8 40.3 38.7 100 39.2 39.7 38.9 38.7 38.2 120 39.438.2 38.3 38.8 38.5 200 38.2 37.5 37.6 38.6 38.0 300 37.3 37.9 37.7 38.137.5

According to Table 1, the storage modulus of the acrylic release agentprecursor and the contact angle of the acrylic release agent of Examples1 to 4 are 1.4×10³ to 2.2×10³ Pa and 37.3° to 42.0°, which satisfy therequirements of a storage modulus of 1×10² to 3×10⁶ Pa and a contactangle of no less than 15° disclosed in WO 01/64805 and/or JapaneseUnexamined Patent Publication (Kokai) No. 2001-240775.

Further, as is apparent from Table 1, the peel force within theunderlined range has a given stable value and is preferred. It is foundthat, when the acrylic release agent precursor of Comparative Example 1is not irradiated with ultraviolet radiation in a dose of no less than100 mJ/cm², a release sheet having a desired peel force can not beprovided. On the other hand, the acrylic release agent precursors ofExamples 1 to 4 can provide a release sheet having a desired peel forcein a reduced ultraviolet dose depending on the amount of EBECRYL P36.

All of the release sheets of Examples 1 to 4 have the peel force in thesame level as that of Comparative Example 1 and a detrimental effect onpeel force is not caused by EBECRYL P36, that is, an ultraviolet activegroup. Therefore, the acrylic release agent precursor using 0.8% byweight of EBECRYL P36, like Example 4, can provide a release sheet withfive times more productivity than in the case of Comparative Example 1using no EBECRYL P36, while maintaining the peel force.

Further, the above results suggest that when a dose of ultravioletirradiation required to form a releasing sheet varies depending oncomposition of a releasing agent precursor, the releasing sheet can beproduced with a constant dose of ultraviolet irradiation by adjusting anamount of acrylic ester having a group capable of being activated byultraviolet radiation to be added.

Examples 5 to 8

In the same manner as in Examples 1 to 4, except that4-acryloyloxybenzophenone (ABP) was used as the acrylate ester havingbenzophenone in place of EBECRYL P36 in these examples, acrylic releaseagent precursors were prepared and release sheets were produced andevaluated. The peel forces of these release sheets at various acrylicrelease agent precursors and ultraviolet energy densities are shown inTable 2.

TABLE 2 Example No. Comparative Example 5 Example 6 Example 7 Example 8Example 1 Composition ISA/ABP (wt %/wt %) 100/0.03 100/0.1 100/0.4100/0.8 100/0 Storage elastic modulus (Pa) of release agent precursor UVdose (mJ/cm²) 1.2 × 10³ 2.2 × 10³ 1.1 × 10³ 1.6 × 10³ 1.2 × 10³ Peelforce (N/25 mm) 10 — 13.2  0.15  0.15 — 20 —  1.1  0.15  0.17 — 30  8.7 0.67  0.15  0.18 — 40  1.6  0.17  0.15  0.18  7.9 60  0.19  0.16  0.16 0.19  3.6 80  0.19  0.16  0.17  0.20  1.9 100  0.19  0.16 — —  0.16 120 0.17  0.16 — —  0.17 200  0.16  0.14 — —  0.16 300 — — — —  0.17Contact angle 10 40.7 41.4 41.2 41.6 39.9 (degree) 20 40.7 40.8 41.541.3 39.7 30 39.8 40.5 41.3 40.7 39.9 40 40.2 41.1 40.8 37.9 39.8 6039.7 40.6 40.2 38.4 39.1 80 39.6 39.7 40.4 38.3 38.7 100 39.0 38.8 39.537.7 38.2 120 38.5 38.4 39.1 37.1 38.5 200 38.6 37.5 38.1 36.4 38.0 30036.8 36.4 37.7 36.7 37.5

According to Table 2, the storage modulus of the acrylic release agentprecursor and the contact angle of the acrylic release agent of Examples5 to 8 are 1.1×10³ to 2.2×10³ Pa and 36.4° to 41.6°, which satisfy therequirements of a storage modulus of 1×10² to 3×10⁶ Pa and a contactangle of no less than 15° disclosed in WO 01/64805 and/or JapaneseUnexamined Patent Publication (Kokai) No. 2001-240775, as in case ofExamples 1 to 4.

Further, as is apparent from Table 2, the peel force within theunderlined range has a given stable value and is preferred. As isapparent from Table 2, when using ABP in the acrylic release agentprecursor, a release sheet having a stable desired peel force can beprovided in a reduced ultraviolet dose depending on the amount of ABP,similar to the case of EBECRYL P36 in Table 1. Also all of the releasesheets of Examples 5 to 8 have the peel force in the same level as thatof Comparative Example 1 and a detrimental effect on peel force is notcaused by ABP, that is, an ultraviolet active group.

Comparative Example 2

In the same manner as in Comparative Example 1, except that 0.1% byweight of benzophenone (BP) was further added to a diluted solutioncontaining an acrylic release agent precursor of 100 parts of an NKester ISA in this example, a release sheet was produced and evaluated.

Comparative Example 3

In the same manner as in Comparative Example 1, except that 0.5% byweight of benzophenone (BP) was further added to a diluted solutioncontaining a polymer of 100 parts of an NK ester ISA to prepare anacrylic release agent precursor in this example, a release sheet wasproduced and evaluated.

The peel forces of the release sheets at various acrylic release agentprecursors and ultraviolet energy densities are shown in Table 3.

TABLE 3 Example No. Comparative Comparative Comparative Example 2Example 3 Example 1 Composition UV dose ISA/BP (mixture) (wt %/wt %)(mJ/cm²) 100/0.1 100/0.5 100/0.0 Peel force 40 10.1  9.6  7.9  (N/25 mm)60 7.3  6.1  3.6  80 2.6  2.8  1.9  100 0.17 0.18 0.16 120 0.19 0.180.17 200 0.16 0.17 0.16

As is apparent from Table 3, the acrylic release agent precursors ofComparative Examples 2 and 3 are irradiated with ultraviolet radiationin the same level as in Comparative Example 1, thus making it possibleto provide a release sheet only in the same level as in ComparativeExample 1. On the other hand, the acrylic release agent precursor ofExample 1 can provide a release sheet in a reduced ultraviolet dose byintroducing an ultraviolet active group into a molecule using only 0.03%by weight of EBECRYL P36. Therefore, it has been found that theultraviolet irradiation dose is not reduced and an increase inproductivity can not be expected merely by adding benzophenone. That is,the poly(meth)acrylate ester having an ultraviolet active groupcontained in the acrylic release agent precursor of the presentinvention is essentially different from a mere mixture of apoly(meth)acrylate ester and a free radical generating agent having anultraviolet active group and the acrylic release agent precursor of thepresent invention can increase the productivity of the release agent.

The acrylic release agent precursor of the present invention make itpossible to efficiently prepare an acrylic release agent in acomparatively small ultraviolet dose regardless of the component.

1. An acrylic release agent precursor comprising a poly(meth)acrylate ester having a group that generates a free radical in the release agent precursor by irradiation with ultraviolet radiation and has a storage elastic modulus of 1×10² to 3×10⁶ Pa at 20° C. and a frequency of 1 Hz, wherein said precursor, after irradiation with ultraviolet radiation, has a contact angle of 15° or more to a mixed solution of methanol and water at a volume ratio of 90/10 and having a wetting tension of 25.4 N/m.
 2. The acrylic release agent precursor according to claim 1, wherein the group that generates the free radical in the release agent precursor by irradiation with ultraviolet radiation is benzophenone.
 3. A release agent article comprising a substrate and the release agent precursor of claim 2 formed on the substrate, wherein the release agent precursor has been irradiated with ultraviolet radiation.
 4. The release agent article of claim 3, wherein the poly(meth)acrylate ester is derived from a monomer component containing a first alkyl (meth)acrylate having a C₁₂₋₃₀ alkyl group, a second alkyl (meth)acrylate having a C₁₋₁₂ alkyl group, and a (meth)acrylate ester having a group that generates a free radical in the release agent precursor by irradiation with ultraviolet radiation.
 5. The release agent article of claim 3, wherein the poly(meth)acrylate ester is derived from a monomer component containing an alkyl (meth)acrylate having a branched C₈₋₃₀ alkyl group, and a (meth)acrylate ester having a group that generates a free radical in the release agent precursor by irradiation with ultraviolet radiation.
 6. The acrylic release agent precursor according to claim 1, wherein the poly(meth)acrylate ester is derived from a monomer component containing a first alkyl (meth)acrylate having a C₁₂₋₃₀ alkyl group, a second alkyl (meth)acrylate having a C₁₋₁₂ alkyl group, and a (meth)acrylate ester having a group that generates a free radical in the release agent precursor by irradiation with ultraviolet radiation.
 7. The acrylic release agent precursor according to claim 1, wherein the poly(meth)acrylate ester is derived from a monomer component containing an alkyl (meth)acrylate having a branched C₈₋₃₀ alkyl group, and a (meth)acrylate ester having a group that generates a free radical in the release agent precursor by irradiation with ultraviolet radiation.
 8. A process for producing an acrylic release agent article, which comprises the steps of: coating a substrate with an acrylic release agent precursor which contains a poly(meth)acrylate ester having a group that generates a free radical in the release agent precursor by irradiation with ultra violet radiation and has a storage elastic modulus of 1×10² to 3×10⁶ Pa at 20° C. and a frequency of 1 Hz, and irradiating the acrylic release agent precursor with ultraviolet radiation to form an acrylic release agent layer having a contact angle of 15° or more to a mixed solution of methanol and water at a volume ratio of 90/10 and having a wetting tension of 25.4 N/m. 